McKenna Turns Ten!: S'mores Cake

Even though I decided to devote my furlough to yeasted dough baking projects, I did make a few exceptions. One was a 10th birthday cake for McKenna, the oldest daughter of our friends Jim and Colleen. I usually don't get to make her cake since her birthday is right after Christmas and we are always gone for the holidays. But this year she had a birthday party in January during her school break -- and even though it was a weekday, being furloughed meant I had time to bake.

McKenna specifically asked for a s'mores cake. I instantly thought of a recipe from Stella Parks (aka BraveTart) published in The New York Times in late 2017 for a Devil's Food Cake with Toasted Marshmallow Frosting. I figured that I could convert the dessert to a s'mores cake if I added some graham cracker components, so I incorporated some graham crumbs and graham buttercream (both from Christina Tosi's All About Cake), as well as some miniature s'mores for decoration.

First I made the graham crumbs. They're a mixture of ground graham crackers, milk powder, sugar, salt, melted butter, and heavy cream. The mixture forms small clusters that you bake in a low oven. I set aside some of the graham crumbs to use as is but also turned some of them into graham buttercream. For the buttercream, you blend graham crumbs with milk until smooth, and add in softened butter, powdered sugar, light brown sugar, and salt. My mixture was way too runny to use a frosting, so I ended up adding more butter until I could get it to thicken up a little.

The devil's food cake is a one-bowl cake that is the same devil's food recipe in Stella's cookbook BraveTart. Actually, there is one significant (to me) difference in the cookbook version, so I'm glad I looked at the book instead of The New York Times version. The cookbook specifies that the six eggs in the batter should be cold, straight from the fridge. Generally if a recipe does not specify any temperature for eggs, I bring them to room temperature first. So I would have done the same here if I hadn't been using the cookbook. Anyway, to make the batter you heat coffee and butter in a large saucepan until the butter melts; remove from the heat and whisk in Dutch-process cocoa and finely chopped dark chocolate, followed by brown sugar, vanilla, and salt; add cold eggs and egg yolks; and mix in sifted flour and baking soda. I divided the batter between three parchment lined 8-inch pans to bake.

The marshmallow frosting is a Swiss meringue that you make by beating egg whites with sugar, salt, cream of tartar, and vanilla in a bowl set over simmering water until the mixture reaches 175 degrees. Then you transfer the meringue to a stand mixer and whisk until glossy and thick.
To assemble the cake, I leveled all of the cooled layers and gathered up my freshly made marshmallow frosting, freshly made graham buttercream, and the graham crumb clusters. I topped the first cake layer with marshmallow frosting and sprinkled on a generous amount of graham crumbs. I stacked on the second cake layer and spread on the graham buttercream, followed by marshmallow frosting. Then I added the final cake layer, spread on marshmallow frosting, and sprinkled on graham crumbs that I covered with more marshmallow frosting before covering the sides with marshmallow as well.

I used a small butane touch to brown the marshmallow, but if you look at the photo above, you can see that I didn't toast the bottom portion of the buttercream. This is because I had put the cake on a masonite cake board wrapped in Wilton Fanci-Foil, which is paper-backed food safe foil. Since the backside is paper, I was afraid I might set it on fire if I got the flame too close. So unfortunately I had to leave the band around the bottom untoasted. I threw a few graham crumbs on top of the cake as well, and the final garnish was some miniature s'mores -- squares of graham crackers that I cut down to size, mini marshallows that I toasted with a kitchen torch, and a small piece of chocolate.
I put the cake in a cake box and drove to Jim and Colleen's house with the box in the trunk of my car. When I opened up the box after arriving, I was disappointed to see that the top two layers of the cake had shifted slightly (maybe half an inch) off of the bottom layer. The cake wasn't in danger of collapsing, but there wasn't anything I could do to re-align the layers without ruining the toasted finish on the marshmallow frosting. Fortunately, McKenna and her friends did not seem to mind. I didn't actually eat a piece of this cake, but Jim gave it a rave review, especially the crunchy graham crumb component. I recently used this same cake recipe to make cupcakes for a baby shower (I paired them with Rose Levy Beranbaum's chocolate neoclassic buttercream), and they were delicious. Not overly rich, but nicely chocolate-y and very satisfying.

In any case, I am happy that I was able to fulfill McKenna's s'mores cake wish!

Recipes: "Devi's Food Cake with Toasted-Marshmallow Frosting" by Stella Parks, recipe available here from The New York Times (the components are the "Devil's Food Cake" and "Marshmallow Meringue" recipes from BraveTart) "Graham Crumbs" and Graham Buttercream" from All About Cake by Christina Tosi.